Current minimally invasive medical devices for use in operations such as retrieval or biopsy are typically operated by mechanical means, using a pull wire. Typically, a distal end of the pull wire connects to an end-effector, such as a basket-type retrieval device, a grasper, a biopsy device, etc. Generally, the proximal end of the pull wire is connected to a control or actuation mechanism in the handle of the medical device.
The pull wire typically transmits movement in a control or actuation mechanism in the handle of the device to the end-effector. Through use of such a pull wire, or a series of pull wires, the end-effector can be controlled to extend from the end of a sheath, retract into the sheath, cut away a sample for a biopsy, or to take other actions that are typically performed by devices such as graspers, basket-type retrieval devices or biopsy devices.
The pull wire in these devices is typically made of metal, and is often somewhat rigid. This rigidity can make it more difficult to maneuver the medical device within the body.
Additionally, use of a pull wire and actuation mechanisms associated with the pull wire add substantially to the number of component parts of a minimally invasive medical device. This increases the cost and complexity of the device, and increases the chance of failure of the device.
Minimally invasive medical devices that use actuation means other than a pull wire have been developed. For example, some devices use compressed gas to propel a needle, biopsy device, or other medical device. Such pneumatically-actuated medical devices typically use a “firing trigger” mechanism to trigger the release of the compressed gas. Such mechanisms provide very little control, and are typically only able to perform the single action of rapidly propelling a device such as a needle.
While this lack of control may be acceptable for some procedures, many medical procedures require fine control over the rate, timing, and precise positioning of a device. Other applications for minimally invasive medical devices require more varied action than simply propelling a portion of the device forward. For example, many procedures require a medical device that can be controllably extended and retracted. Devices that use compressed gas and “firing triggers” typically do not provide such fine control or varied actions.